The present invention relates to a suspension apparatus for a vehicle, such as an automobile.
Generally, in a suspension apparatus for an automobile, comprising a hydraulic shock absorber generating damping force, a small damping force is desired while driving in a straight line, from the viewpoint of ease in absorbing vibration and obtaining good riding quality. On the other hand, a large damping force is desired during braking, acceleration or cornering, from the viewpoint of suppressing pitching and rolling of the vehicle body and obtaining good steering stability. Therefore, there has been conventionally employed a suspension control apparatus comprising: a hydraulic shock absorber capable of controlling a damping force; an actuator for switching the damping force; a controller which controls an operation of the actuator; and various sensors which detect an acceleration of the vehicle body, etc. In this suspension control apparatus, the damping force is controlled appropriately according to a road surface condition, a vehicle running condition, etc., so as to obtain good riding quality and steering stability.
The above-mentioned suspension control apparatus requires use of various electronic devices, such as the controller and the actuator. These electronic devices are expensive, and further require costs for ensuring reliability of the devices. As a countermeasure, Unexamined Japanese Patent Application Public Disclosure No. 10-213171 proposes a suspension apparatus in which hydraulic shock absorbers provided at left and right wheels of a vehicle are connected through a pipe to each other. In this apparatus, a spool provided in a piston rod in the hydraulic shock absorber is moved by utilizing a difference in hydraulic pressure in the left-handed and right-handed hydraulic shock absorbers, to thereby adjust a damping force of the hydraulic shock absorber automatically according to a vehicle running condition.
Thus, there has been an increasing demand for a suspension apparatus which is capable of adjusting a damping force of the hydraulic shock absorber mechanically and automatically according to a vehicle running condition, without using electronic devices such as a controller and an actuator. In addition, it has been required to develop a suspension apparatus which has a simple construction and which is capable of generating an appropriate damping force according to a vehicle running condition, by adjusting damping force characteristics in a wide range.